/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */

package org.apache.iotdb.tsfile.encoding.encoder;

import org.apache.iotdb.tsfile.common.conf.TSFileConfig;

import java.io.ByteArrayOutputStream;

/**
 * Encoder for int value using gorilla encoding.
 */
public class DoublePrecisionEncoderV1 extends GorillaEncoderV1 {

    private long preValue;

    public DoublePrecisionEncoderV1() {
        // do nothing
    }

    @Override
    public void encode(double value, ByteArrayOutputStream out) {
        if (!flag) {
            // case: write first 8 byte value without any encoding
            flag = true;
            preValue = Double.doubleToLongBits(value);
            leadingZeroNum = Long.numberOfLeadingZeros(preValue);
            tailingZeroNum = Long.numberOfTrailingZeros(preValue);
            byte[] bufferLittle = new byte[8];

            for (int i = 0; i < 8; i++) {
                bufferLittle[i] = (byte) (((preValue) >> (i * 8)) & 0xFF);
            }
            out.write(bufferLittle, 0, bufferLittle.length);
        } else {
            long nextValue = Double.doubleToLongBits(value);
            long tmp = nextValue ^ preValue;
            if (tmp == 0) {
                // case: write '0'
                writeBit(false, out);
            } else {
                int leadingZeroNumTmp = Long.numberOfLeadingZeros(tmp);
                int tailingZeroNumTmp = Long.numberOfTrailingZeros(tmp);
                if (leadingZeroNumTmp >= leadingZeroNum && tailingZeroNumTmp >= tailingZeroNum) {
                    // case: write '10' and effective bits without first leadingZeroNum '0'
                    // and last tailingZeroNum '0'
                    writeBit(true, out);
                    writeBit(false, out);
                    writeBits(
                            tmp, out, TSFileConfig.VALUE_BITS_LENGTH_64BIT - 1 - leadingZeroNum, tailingZeroNum);
                } else {
                    // case: write '11', leading zero num of value, effective bits len and effective
                    // bit value
                    writeBit(true, out);
                    writeBit(true, out);
                    writeBits(leadingZeroNumTmp, out, TSFileConfig.LEADING_ZERO_BITS_LENGTH_64BIT - 1, 0);
                    writeBits(
                            (long) TSFileConfig.VALUE_BITS_LENGTH_64BIT - leadingZeroNumTmp - tailingZeroNumTmp,
                            out,
                            TSFileConfig.DOUBLE_VALUE_LENGTH - 1,
                            0);
                    writeBits(
                            tmp,
                            out,
                            TSFileConfig.VALUE_BITS_LENGTH_64BIT - 1 - leadingZeroNumTmp,
                            tailingZeroNumTmp);
                }
            }
            preValue = nextValue;
            leadingZeroNum = Long.numberOfLeadingZeros(preValue);
            tailingZeroNum = Long.numberOfTrailingZeros(preValue);
        }
    }

    private void writeBits(long num, ByteArrayOutputStream out, int start, int end) {
        for (int i = start; i >= end; i--) {
            long bit = num & (1L << i);
            writeBit(bit, out);
        }
    }

    @Override
    public void flush(ByteArrayOutputStream out) {
        encode(Double.NaN, out);
        clearBuffer(out);
        reset();
    }

    @Override
    public int getOneItemMaxSize() {
        // case '11'
        // 2bit + 6bit + 7bit + 64bit = 79bit
        return 10;
    }

    @Override
    public long getMaxByteSize() {
        // max(first 8 byte, case '11' 2bit + 6bit + 7bit + 64bit = 79bit )
        // + NaN(2bit + 6bit + 7bit + 64bit = 79bit) =
        // 158bit
        return 20;
    }
}
